Snakes in the Plane: Direct Imaging of Interstellar Turbulence

Monday 3pm in Parnell (7) 234

Speaker: Professor Bryan Gaensler (CAASTRO/University of Sydney)
Date: 21st May 2012

The interstellar medium (ISM) of the Milky Way consists of gas and dust at a range of temperatures and pressures, and provides the raw material from which stars and planets form. Astronomers have developed a sophisticated understanding of the ISM as a multi-phase, magnetised, turbulent medium. However, observations have lacked the sensitivity and resolution to directly image the small-scale structure associated with turbulent motions in the diffuse ISM. Radio polarimetry is a promising avenue for further progress, because Faraday rotation of linearly polarised radio signals provides a very sensitive probe of fluctuations in magnetic field and ionised gas density. I will describe a new way of processing images of linearly polarised radio emission from the ISM, in which I have derived the gradient of the Stokes vector. This provides the first direct image of supersonic turbulence in the ISM, manifested as a complex filamentary web of sharp jumps in gas density and magnetic field. Application of the polarisation gradient to both simulations and observations can allow the measurement of currently unconstrained parameters of interstellar turbulence such as the Mach number, Reynolds number and magnetic field strength.